I have around £150 which translates to about 230$ which I want to spend on my fixed gear bike, I want to get a part which I wont have to upgrade for a long time, my current bike is:

State black label frame
BLB af02 full carbon forks
deda dabar carbon bars
deda superleggero stem
sram s100 cranks
state bicycle saddle
state bicycle wheels
state seat post
taurus mtb pedals

What should i change on my bike? I was possibly thinking some sram omnium cranks?

Open to any suggestions, thanks!

A new saddle? I don't know how comfortable you are with the current one, but that would be my first upgrade.

Yeah, possibly it's not the most comfortable thing in the world..

Most bang for your buck? Changing out your wheels for something lighter. Wabi wheels are known for being a very good deal for the money and are some of the lightest you can get in that price range. You will have to save up a bit more for international shipping but still definitely worth it. The owner, Richard, is incredibly helpful as well. Some guys on your side of the pond might know of other options locally though.

Wabi Cycles fixed gear wheels

Rubber pneumatic tires mounted to the rims and inflated with fifty or more psi of air will be a pretty huge upgrade.

I would also consider upgrading the cranks. I have stock state cranks on my core state, and my SO has S100 on hers, and the stock ones are actually better. I would recommend the S300s though, they're a really solid crank.

Contact points first, seat, grips, pedals. Then wheels and tires. Later gear assembly